Such a private branch exchange and a method of the above-mentioned type for its operation are known, for example, from article V. Hilt et al., “Approaches to Implementing Services in SIP Networks”, Bell Labs Technology, Bell Laboratories, Murray Hill, N.J., US, volume 9, No. 3, pages 39 to 44.
In modern telecommunication or telephone installations or systems, such as, for example, call centers, usually a multitude of telephony or communication terminals are connected with a central exchange unit, through which telecommunication connections between individual communication terminals or else of calls coming in from outside the internal communication networks, with selected telecommunications terminals. Within the framework of these telecommunication connections, voice or user data are transmitted to the respective selected communication terminal and/or from said terminal to the central exchange device and from the latter, to the respective terminal. This data transmission can take place conventionally or using the Internet Protocol. The communications terminals provided can be installed telephony or data terminals or handsets or else telephony or data terminals connected to the exchange device via a wireless communication connection.
Such private branch exchanges, in particular for call centers or contact centers, can in particular also be designed for a data transfer through multimedia applications or in particular also through the Internet protocol. In such telecommunication networks, whose communications terminals can be connected with each other and with the central exchange device in a wire-bound manner or by means of wireless technology, a user has a multitude of applications or services at his disposal, and a relatively high and complex number of secondary functions, such as, for example, acquisition of telephone rates, call release, call forwarding or the like, provided in connection with the setup of a communication connection, can be offered. Such private branch exchanges with a multitude of integrated and offered further applications or services are usually also designed as an intelligent network or as a so-called integrated multimedia system (IMS), whereby especially in such integrated multimedia systems, the users are offered voice-over-IP telephony, automatic answering functions (voice mail), multimedial message transfer, such as, for example, instant messaging (IM), so-called push-to-talk (PTT) services, conference calls (net meetings) and the like, as additional functions, applications or services. These services or applications are usually provided as part of the respective IMS by allocated data-processing systems, the execution of such functions being controlled by a higher-ranking communication-management module of the IMS, the so-called “session manager” (SM).
To manage secondary functions and connection modalities which have to be taken into account in the setup and maintenance of a communication connection between different communication terminals, such as, for example, telephone-rate monitoring, releases for the dialing of telephone numbers, the protocols to be utilized in data transfer, and the like, appropriate application-management modules, also called “application servers” (AS), are usually allocated to the individual communication terminals. These are also part of the integrated multimedia systems.
To set up a communication connection in modem private branch exchanges, the so-called session-initiation protocol (SIP) can be utilized, whereby the communication modalities are agreed, prior to setting up the communication connection properly speaking, through an appropriate data exchange between the communication terminals involved, i.e. in particular the calling communications terminal and the desired target communications terminal. In an integrated multimedia system of the above-described type, the invite message is usually transmitted, after activation of the calling communication terminal and the input of the desired target telephone number by the user, via the higher-ranking communication-management module or the session manager to the allocated application-management module in the form of a so-called invite message. After the connection modalities for the calling communications terminal, i.e., in particular releasing options and the like, have been verified by the allocated application-management module or the allocated application server, the invite message is appropriately forwarded via the session manager.
The integrated multimedia system can be designed in particular as a so-called “full-call model” system. In such systems, the application-management module or the application server is designed for verifying, in case of an invite message forwarded by the session manager or by the higher-ranking communication-management module, all modalities and connection parameters of the desired communication connection, i.e., both for the calling and for the called side, and to initiate, if necessary, appropriate reactions, such as releases or the like. In such a concept, such a full-call application server carries out the connection modalities for both the calling communications terminal and the called target communications terminal. Thus, the corresponding application server verifies and possibly carries out the necessary verifications, releases and other reactions concerning both the calling communications terminal and the target side of the desired communication connection, i.e. of the called communications terminal.
Such integrated multimedia systems based on a so-called full-call model are meanwhile relatively common, offering the possibility that the respective allocated application server, designed in the manner of a central exchange device, manages in particular communication connections internal to the organization, making use of the session-initiation protocol.